Once and for all, what relevance remains to the TSH levels in absence of the thyroid?

Especially when treated with T3/combo, known to suppress TSH...why on earth medics would insist on this indicator instead of, for example, FT3 and FT4

I am on a T4/T3 combo and for some time now I have dropped under the minimum TSH level; I felt good on a 0.3 to 1 interval but sometimes, like a rollercoaster, I had small and medium crashes. Now it's suppressed, 0.1 last value recorded, but I am constantly well, symptom wise.

Still, my doctor's appointment is due next week and she will comment on my latest TSH value, therefore I need munitions to counter it.

This post's objective is that I would like to:

a) document TSH relevance after TT, explanation being the prioroty but, if possible, please point me to reliable/scientific/peer reviewed sources

b) learn, when selfdosing like I do, what should I take into consideration, besides my current indicators: symptoms, FT3 & FT4 and, on another side conversion enablers like vits+minerals (b12, d3, Fe, Ca, B6)

Thank you, kind regards and best of health

Read more about...

Your pituitary gland doesn't know that your thyroid gland has been removed so it will continue issuing TSH when it detects low thyroid hormone levels and will shut off TSH when it detects sufficient thyroid hormone. So, TSH can be used to indicate undermedication and perhaps overmedication, although FT4 and/or FT3 should be tested to confirm overmedication.

You are not feeling well because TSH is 0.3 or 0.1. TSH won't make you feel anything. It will be your FT3 level when TSH is 0.3 or 0.1 which makes you feel well. As long as FT3 remains within range you are not overmedicated even though TSH is suppressed. You should be aware that suppressed TSH may increase the risks of developing osteoporosis and atrial fibrillation though. I have informed my endo that I prefer to feel well today on my current doses which suppress TSH and accept that it may increase my risk of having adverse health outcomes in the future.

While I've read that good levels of vitamin D aid conversion, I'm not aware that the other vits/minerals have any effect on conversion. Low ferritin can make it difficult to tolerate sufficient thyroid replacement causing hyper symptoms with hypo labs.

Ferritin, vitamin D, B12 and folate are commonly low in hypothyroid patients and symptoms may be confused with hypothyroid symptoms so its worth testing them.

I used the wonder why TSH was so important if it did nothing at all in the case of a TT.

It is a terrible measure of cellular status. The only reason to be concerned with TSH is that it evidently plays a role in up or down regulating the deioninases that control T4 conversion. So a really low TSH will favor conversion to RT3 rather than T3. It isn't always something you can change (mine is suppressed at the sight of T3 meds), but at least you can know what is going on and adjust the ratio of T4/T3 supplementation. Here is a link that I believe has a couple of studies showing the relationship.